1. Field of the Invention
The present invention relates to a demodulating apparatus, a demodulating method, and a computer program, and, more particularly to a demodulating apparatus, a demodulating method, and a computer program for reducing time during which a video is not displayed at the time of tuning in a digital television broadcast.
2. Description of the Related Art
In recent years, a television broadcast is being changed from a terrestrial analog broadcast (hereinafter referred to as analog broadcast as appropriate) to a terrestrial digital broadcast (hereinafter referred to as digital broadcast as appropriate). In the digital broadcast, processing different from processing in the analog broadcast such as modulation and demodulation is performed on a transmission side and a reception side. When data of a program (data of video and sound) is modulated on the transmission side, data (parameters) concerning the modulation is transmitted from the transmission side to the reception side together with the data of the program.
A structure of an example of a receiving apparatus in the past will be explained with reference to FIG. 1. A receiving apparatus 10 shown in FIG. 1 has a function of receiving and processing a program provided by a digital television broadcast. In the following explanation, the “digital television broadcast” is abbreviated as “digital broadcast” as appropriate.
The receiving apparatus 10 shown in FIG. 1 includes a tuner unit 21, an A/D (Analog/Digital) conversion unit 22, a symbol synchronizing unit 23, an FFT (Fast Fourier transform) unit 24, a TMCC (Transmission & Multiplexing Configuration Control) detecting unit 25, a frequency deinterleaving unit 26, a time deinterleaving unit 27, a demapping unit 28, a bit deinterleaving unit 29, a Viterbi decoding unit 30, a byte deinterleaving unit 31, an energy de-spreading unit 32, and an RS decoding unit 33.
The digital broadcast broadcasted by a broadcasting station is received by a not-shown antenna and supplied to the tuner unit 21 as an RF (Radio Frequency) signal. The tuner unit 21 frequency-converts the RF signal supplied from the antenna into an IF (Intermediate Frequency) signal and filters the IF signal with a band-pass filter (BPF) built therein.
The filtered IF signal is supplied to the A/D conversion unit 22. The A/D conversion unit 22 A/D-converts the IF signal supplied and supplies the IF signal digitized to the symbol synchronizing unit 23. The symbol synchronizing unit 23 orthogonally demodulates the IF signal supplied using a carrier wave signal of a predetermined frequency (a carrier wave frequency) and generates an OFDM signal of a base band.
The OFDM signal (an OFDM time domain signal) of the base band generated is set as a complex signal including a real axis component (an I channel signal) and an imaginary axis component (a Q channel signal). Processing for calculating a boundary of an OFDM symbol of the base band, processing for setting arithmetic operation start timing for an FFT arithmetic operation in the FFT unit 24, and the like are also executed.
The FFT unit 24 extracts a signal for an effective symbol length from the OFDM time domain signal and applies the FFT arithmetic operation to the signal extracted. The signal from the FFT unit 24 is supplied to the TMCC detecting unit 25. The TMCC detecting unit 25 detects TMCC information from the signal supplied.
The frequency deinterleaving unit 26 applies deinterleave processing in a frequency direction to the signal supplied and supplies a signal after the deinterleave processing to the time deinterleaving unit 27. The time deinterleaving unit 27 applies, in accordance with the TMCC information supplied, deinterleave processing in a time direction to the signal supplied from the frequency deinterleaving unit 26 and supplies a signal after the deinterleave processing to the demapping unit 28.
The demapping unit 28 applies, in accordance with the TMCC information supplied, reallocation processing (demapping processing) for data to the signal carrier-demodulated (the complex signal) supplied from the time deinterleaving unit 27 and restores a transmission data sequence. For example, the demapping unit 28 performs demapping processing corresponding to QPSK, 16QAM, or 64QAM. The demapping unit 28 supplies the transmission data sequence restored to the bit deinterleaving unit 29.
The bit deinterleaving unit 29 applies deinterleave processing corresponding to bit interleave for error distribution of a multivalue symbol to the transmission data sequence supplied from the demapping unit 23 and supplies a signal after the deinterleave processing to the Viterbi decoding unit 30. The Viterbi decoding unit 30 applies Viterbi decode processing for decoding of a convolutional-coded bit string to the signal supplied and supplies a signal after the Viterbi decode processing to the byte deinterleaving unit 31.
The byte deinterleaving unit 31 applies deinterleave processing in a unit of byte to the signal supplied from the Viterbi decoding unit 30 and supplies a signal after the deinterleave processing to the energy de-spreading unit 32. The energy de-spreading unit 32 applies energy -de-spreading processing corresponding to energy diffusion processing to the signal supplied from the byte deinterleaving unit 31 and supplies a signal after the energy de-spreading processing to the RS decoding unit 33.
The RS decoding unit 33 applies Reed-Solomon (RS) decode processing to the transmission data sequence supplied and outputs the transmission data sequence as a transport stream defined by the MPEG-2 systems.
Processing by the time deinterleaving unit 27 will be explained. As shown in FIG. 1, the time deinterleaving unit 27 is provided at a post-stage of the frequency deinterleaving unit 26. The TMCC information detected by the TMCC detecting unit 25 is supplied to the time deinterleaving unit 27. The signal subjected to the deinterleave processing in the frequency direction is also supplied to the time deinterleaving unit 27 from the frequency deinterleaving unit 26.
The time deinterleaving unit 27 rearranges signals of an amount based on parameters included in the TMCC information. Therefore, according to the supply of the TMCC information, the time deinterleaving unit 27 starts to accumulate the signals in a buffer having a capacity corresponding to the parameters and, when a necessary amount of signals are accumulated, outputs the data rearranged. In other words, after the TMCC information is detected by the TMCC detecting unit 25 and supplied to the time deinterleaving unit 27, the processing by the time deinterleaving unit 27 is started.
In this way, on the reception side, when data of a program is demodulated, processing for demodulation is executed with reference to parameters transmitted to the reception side. The parameters transmitted and received include the TMCC signal as described above. The TMCC signal (TMCC information) is transmission multiplexing control signal and includes designation of a transmission system (designation of a modulation system and an error correction coding ratio, etc.) and information for transmitting a slot number for managing plural transport streams.
In order to acquire the TMCC information, since the TMCC signal (the TMCC information) has the length of one frame that is a temporal unit of a broadcast signal, it is necessary to acquire (receive) at least data for one frame. Therefore, for example, when a user tunes in a channel of the digital broadcast, it may be impossible to start the time deinterleave processing and perform change of a channel (start provision of a video to the user) until the TMCC information is received.
In order to reduce such time during which the user is not provided with a video, JP-A-2003-51795 proposes to store TMCC information detected when program data or the like is received last time and use the TMCC information for demodulation of program data received this time.